1. Field of the Invention
This invention relates to packing rings, a method for the production of a packing ring.
2. Description of the Prior Art
Packing rings can be used extensively as seal members in parts prone mainly to rotary or reciprocating sliding motions or as seal members in stationary parts. For example, they can be used in a seal device to be interposed between the body or bonnet and the stem of a valve or in a seal device for fluid-handling devices and to be incorporated in a pump shaft sealing part, etc. Examples of the fluids for which the packing rings are effectively used include gases, liquids and loose solid materials. Particularly in recent years, the free emission of fluids from fluid-handling devices has posed a serious problem from the standpoint of preservation of the earth's environment. From this point of view, there is a great demand for developing packing rings which excel in heat resistance and chemical resistance as well as in fast sealing properties.
Known packing rings are generally are of two types. Those of one type are produced by cutting a ribbon from a sheet of expanded graphite, winding the ribbon into a spiral roll and compression molding the roll annularly in a die, and those of the other type are produced by laminating a plurality of sheets of expanded graphite and punching a ring of prescribed dimensions out of the resultant lamination.
The packing rings of the two types are inserted in an empty space adapted for accommodation thereof and then compressed therein prior to use.
In the case of the packing rings of the former type, since they easily deform laterally, namely in the radial direction, under the force of the compression, they gain in force of contact with a stuffing box or a shaft and consequently manifest a sufficient sealing function even when the stuffing box or shaft lacks the or when surfaces thereof are machined inaccurately. However, such satisfactory sealing function tends to decline with the elapse of time because the packing rings easily protrude through gaps such as occur between the bottom surface of the stuffing box and the shaft, between the gland retainer and the shaft and between the gland retainer and the empty space of the stuffing box, and consequently entails a loss in the force of compression.
Further, since the fastness of adhesion between the layers of the laminated sheet material forming the packing rings is rather degraded than exalted by the force of the compression exerted on the packing rings, the fluid being handled is liable to permeate the packing rings in the axial direction. Besides, the surfaces of the packing rings which contact other packing rings, the bottom surface of the stuffing box, or the retaining surface of the gland retainer are formed of the end faces of the sheet material which forms the packing ring. Thus, the packing rings betray poor fastness of adhesion on the surfaces in question and tend to get wet, and the surfaces themselves tend to sustain injury and demand delicate handling.
In the case of the packing rings of the latter type, such packing rings do not gain very much in force of contact with the stuffing box or the shaft because the ratio at which the packing rings are deformed laterally, namely in the radial direction, under the force of the compression is very small. When the stuffing box or the shaft lacks dimensional accuracy or when surfaces thereof are machined in accurately, therefore, the packing rings tend to entail leakage of the fluid because of poor fastness of adhesion. Fortunately, these packing rings preclude the permeation of fluid therethrough in the axial direction under the force of compression, manifest satisfactory fastness of adhesion thereof to the bottom surface of the stuffing box or to the retaining surface of the gland retainer, and permit no ready leakage of fluid through the interfaces. Further, these packing rings do not very often protrude through the empty space for accommodating the packing rings, namely through the gap between the bottom part of the stuffing box and the shaft, the gap between the gland retainer and the shaft and the gap between the gland retainer and the stuffing box. The possibility that the packing rings will protrude to the extent of degrading the force of compression and sacrificing the sealing function is remote.
These packing rings are at a disadvantage in entailing easy vertical separation between the layers of laminated sheet material, readily sustaining injury, demanding delicate handling, and requiring substantial and labor for maintenance.
FIG. 18 is a partial longitudinal cross section illustrating a seal device which is disclosed in Japanese Utility Model Publication No. 1-29315. This seal device has been proposed for the purpose of utilizing packing rings of expanded graphite produced by the two methods described above while eliminating the drawbacks thereof and harnessing the advantages thereof.
In FIG. 18, reference numerals 21 to 25 refer to packing rings of expanded graphite, specifically numerals 21 and 25 each represent a packing ring produced by the latter of the two methods and numerals 22, 23 and 24 each represent a packing ring produced by the former method. Reference numeral 26 refer to a stuffing box, numeral 27 a stem, and numeral 28 a gland retainer.
As illustrated in FIG. 18, the packing rings 21 to 25 are compressed with the gland retainer 28 inside the stuffing box 26. As a result, the packing rings 22, 23 and 24 produced by the former method are deformed in the radial direction and brought into tight contact with the stuffing box 26 and the stem 27 to preclude the otherwise possible leakage of fluid along the interfaces of the contact.
The packing rings 21 and 25, in the meanwhile, prevent leakage therethrough of the fluid which has permeated through the packing rings 22, 23 and 24 in the axial direction. Further, the packing rings 21 and 25 prevent leakage therethrough of the fluid which has flowed through the interfaces thereof with the packing ring 22 or 24, a bottom surface 26a of the stuffing box 26, and a retaining surface 28a of the gland retainer 28. Since the packing rings 21 and 25 are superposed in a direction which is perpendicular to the gap A between the bottom part of the stuffing box 26 and the stem 27, the gap B between the gland retainer 28 and the stem 27 and the gap C between the gland retainer 28 and the stuffing box 26, they protrude through these gaps very rarely.
Even in the seal device which is constructed as illustrated in FIG. 18, however, the packing rings 21 through 25 tend to sustain injury and demand delicate handling. Particularly the packing rings 21 and 25 easily separate vertically from the intervening packing rings 22 to 24 and render the maintenance thereof difficult. Though they protrude through the aforementioned gaps A, B and C only slightly, such protrusion nevertheless remains a problem. Moreover, this seal device is at a disadvantage in insufficiently preventing leakage therethrough of a gas of small molecular weight or a solvent of strong osmosis.
A object of the present invention is to provide a method of producing packing rings of expanded graphite that have excellent heat resistance and chemical resistance and that nevertheless eliminate the drawbacks inherent in the conventional packing rings.